JP2012078655A - Plastic rod lens and plastic rod lens array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plastic rod lens which has excellent heat resistance, sufficiently suppresses its thermal contraction even when used under a high-temperature environment, and reduces heat fluctuation in a conjugate length.SOLUTION: A plastic rod lens is obtained by hardening an unhardened material containing a polymer (A) having a constitutional unit derived from an acid anhydride monomer and a radical polymerizable vinyl monomer (B).

Description

  The present invention relates to a plastic rod lens and a plastic rod lens array using the same.

A plastic rod lens (hereinafter sometimes simply referred to as a “rod lens”) is a cylindrical lens having a refractive index distribution in which the refractive index continuously decreases from the center toward the outer periphery. A plastic rod lens array in which a large number of rod lenses are bonded and fixed in one or more rows between two substrates so that the central axes of the rod lenses are substantially parallel to each other. Hereinafter, it may be simply referred to as “rod lens array”), and is widely used for various scanners such as hand scanners, parts for image sensors in copying machines and facsimiles, writing devices such as LED printers, and the like.
As the main material of the rod lens, a composition containing a radical polymerizable vinyl monomer and a polymer soluble in the monomer is often used, and a typical example of the polymer is polymethyl methacrylate. It is.

  A plastic rod lens has a problem that when used in a high temperature environment, the rod lens tends to shrink due to heat. Since the conjugate length changes when the rod lens contracts, the resolution (MTF: moderation transfer function) decreases. In particular, when a lens array composed of plastic rod lenses is used for a high-resolution image sensor or LED printer having a resolution of 600 dpi or more, the problem of resolution reduction becomes serious.

  In Patent Document 1, the heat resistance of a plastic rod lens is improved by performing heat treatment for 1 hour or more at a heat shrinkage start temperature of 100 ° C. or less when the temperature is raised at a rate of temperature rise of 4 ° C./min. A method for suppressing fluctuations in conjugate length when used in an environment is disclosed.

JP 2007-34259 A

  However, the method described in Patent Document 1 does not necessarily have an effect of suppressing a decrease in resolution due to thermal fluctuation of the conjugate length, and a method that can further improve the heat resistance of a plastic rod lens is required.

  The present invention has been made in view of the above circumstances, and a plastic rod lens in which heat shrinkage is sufficiently suppressed even when used in a high temperature environment and the thermal fluctuation of the conjugate length is small, and a plastic made using the same An object is to provide a rod lens array.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors, as a material for a plastic rod lens, include a specific polymer (A) and radical polymerizability that is compatible with the polymer (A). By using the composition containing the vinyl monomer (B), it is possible to provide a rod lens in which thermal shrinkage is further suppressed and thermal fluctuation of the conjugate length is smaller, and by using it, even under a high temperature environment The present inventors have found that a plastic rod lens array excellent in resolution can be provided, and completed the present invention.

That is, the present invention includes the following aspects.
[1] A plastic rod formed by curing an uncured product containing a polymer (A) having a structural unit derived from an acid anhydride monomer and a radical polymerizable vinyl monomer (B). lens.
[2] A plurality of the plastic rod lenses according to [1] includes at least one rod lens array arranged and fixed so that the central axes of the rod lenses are substantially parallel to each other between the two substrates. Plastic rod lens array.

The plastic rod lens of the present invention is excellent in heat resistance, and even when used in a high temperature environment, heat shrinkage is sufficiently suppressed, and thermal fluctuation of the conjugate length is small.
The plastic rod lens array of the present invention is excellent in heat resistance and has a very small reduction in resolution (MTF) when used in a high temperature environment.

Hereinafter, preferred embodiments of the present invention will be described in detail.
<Plastic rod lens>
The plastic rod lens of the present invention is a cylindrical lens having a refractive index distribution in which the refractive index continuously decreases from the center toward the outer periphery. As the refractive index distribution, when the radius of the rod lens is r in a cross section perpendicular to the central axis of the rod lens, the refractive index distribution in the range of 0.2r to 0.8r at least from the central axis toward the outer periphery is as follows. It is preferable to approximate a quadratic curve distribution defined by the following formula (1).
^{_{n (L) = n 0 {}} 1- (g 2/2) L 2} ... (1)
(Where n ₀ is the refractive index (central refractive index) at the central axis of the rod lens, L is the distance from the central axis of the rod lens (0 ≦ L ≦ r), and g is the refractive index of the rod lens. (It is a distribution constant, and n (L) is a refractive index at a position of a distance L from the central axis of the rod lens.)

  The radius r of the rod lens is not particularly limited, but the radius r is preferably small from the viewpoint of compacting the optical system, and the radius r is preferably large from the viewpoint of handling during processing of the rod lens. For this reason, the radius r of the rod lens is preferably in the range of 0.05 to 1 mm, more preferably in the range of 0.1 to 0.5 mm.

The center refractive index n ₀ of the rod lens is 1.4 to 1.6 with respect to light of 525 nm, so that the choice of materials constituting the rod lens is widened, and a favorable refractive index distribution is easily formed. From the viewpoint of
The refractive index distribution constant g of the rod lens is not particularly limited, but is preferably in the range of 0.1 to 2.0 mm ⁻¹ from the viewpoint of compacting the optical system, ensuring the working distance of the optical system, and handling. . If g is 0.1 mm ⁻¹ or less, the working distance of the optical system becomes too long, so that it is difficult to reduce the size of the optical system, and if it is 2.0 mm ⁻¹ or more, the working distance becomes too short. It becomes difficult to design.

  The rod lens of the present invention comprises a polymer (A) having a constitutional unit derived from an acid anhydride monomer (hereinafter sometimes simply referred to as polymer (A)) and a radical polymerizable vinyl monomer. It consists of the hardened | cured material of the uncured material containing (B). The composition of the cured product is not uniform in the radial direction of the rod lens, and the distribution of the composition in the radial direction corresponds to the refractive index distribution and depends on the material of the rod lens and the manufacturing method.

  It is preferable that the rod lens has a light absorption layer containing a light absorber that absorbs at least part of light transmitted through the rod lens on an outer peripheral portion of 0.6r or more from the central axis. In general, with a rod lens, an irregular portion in which the refractive index distribution deviates from the ideal distribution tends to be formed as the distance from the central axis increases, and the optical characteristics due to this are absorbed by the outer periphery of the rod lens. This is because it is suppressed by providing a layer. The thickness of the light absorption layer is preferably 5 μm or more and 100 μm or less. By setting the thickness of the light absorption layer within this range, flare light and crosstalk light can be sufficiently removed and a sufficient amount of transmitted light can be secured.

  As a light absorber to be used, in an image sensor, an LED printer, or the like, a light source that emits light having a wavelength of 400 to 900 nm is generally used as a light source. It is preferable to use one that absorbs light. As such a light absorber, for example, Kayasorb CY-10 manufactured by Nippon Kayaku which absorbs in the 600 nm to near infrared region, Diaresin Blue 4G manufactured by Mitsubishi Chemical which absorbs at 600 to 700 nm, and the like are absorbed at 550 to 650 nm. Examples include Kayset Blue ACR manufactured by Nippon Kayaku Co., Ltd., Mitsui Chemical Dye MS Absorbed at 500 to 600 nm, MS Magenta HM-1450, Mitsui Chemical Dye MS Yellow HD-180 absorbed at 400 to 500 nm, etc. . Moreover, a black dye etc. can be mentioned as a light absorber which absorbs the light of all the wavelength ranges among 400-900 nm. These light absorbers may be used alone or in combination of two or more.

<Method for manufacturing plastic rod lens>
A method for manufacturing the rod lens as described above will be described.
There is no limitation on the method of forming the refractive index distribution of the rod lens, and any method such as an addition reaction method, a copolymerization method, a gel polymerization method, a monomer volatilization method, and an interdiffusion method may be used. In this respect, the interdiffusion method is preferable.
The mutual diffusion method will be described.
First, N types of uncured materials having a refractive index n after curing satisfying n ₁ > n ₂ >...> _{N N} (N ≧ 3) are prepared, and these are sequentially directed from the center toward the outer periphery. The layers are concentrically laminated so as to have a low refractive index and shaped into an uncured long laminate (hereinafter referred to as “filament”). Next, the filamentous material is cured while performing the mutual diffusion treatment of the materials between adjacent layers so that the refractive index distribution between the respective layers of the filamentous material is continuous, or after the mutual diffusion treatment, and the rod lens raw material is cured. A yarn is obtained (spinning process). The interdiffusion treatment refers to giving the filament a thermal history of several seconds to several minutes at 10 to 60 ° C., more preferably 20 to 50 ° C., under a nitrogen atmosphere.

Any of N types of uncured materials constituting the filamentous body contains a polymer (A) having a structural unit derived from an acid anhydride monomer and a radical polymerizable vinyl monomer (B). .
[Polymer (A)]
The polymer (A) may be a homopolymer obtained by polymerizing only an acid anhydride monomer, and may be a monomer copolymerizable with an acid anhydride monomer. It is also possible to use a copolymer (copolymer) obtained by polymerizing a mixture of the above (monomer mixture). In the case of a copolymer, the mass ratio of the mixture of the acid anhydride monomer and the copolymerizable monomer (monomer mixture) can be, for example, 5-30: 95-70. .
Examples of the acid anhydride monomer include maleic anhydride, methacrylic anhydride, acrylic anhydride, 1-cyclopentene-1,2-dicarboxylic anhydride, and itaconic anhydride.
Examples of the monomer copolymerizable with the acid anhydride monomer include methyl methacrylate, styrene, and acrylonitrile.
Examples of the polymer (A) include a homopolymer of maleic anhydride, a copolymer of maleic anhydride, styrene and methyl methacrylate, a copolymer of maleic anhydride and styrene, maleic anhydride, styrene and acrylonitrile. A copolymer of methacrylic acid, a homopolymer of acrylic anhydride, a homopolymer of 1-cyclopentene-1,2-dicarboxylic acid anhydride, and a homopolymer of itaconic anhydride.

The polymer (A) contained in one kind of uncured material may be one kind, or two or more kinds may be used in combination. The polymers (A) contained in each of the N types of uncured materials constituting the filaments may be the same as or different from each other. The viscosity of the uncured product can be adjusted by the type and content of the polymer (A) contained in the uncured product.
N types constituting the filamentous material in that the viscosity of the uncured material can be easily adjusted and a continuous refractive index distribution from the center to the outer periphery can be easily obtained in the rod lens yarn after the mutual diffusion treatment. It is preferable that the refractive indexes of the polymers (A) contained in the uncured product are equal to each other. For that purpose, it is preferable that the polymers (A) contained in the N kinds of uncured materials are the same.

[Radically polymerizable vinyl monomer (B)]
The radical-polymerizable vinyl monomer (B) is only required to be compatible with the polymer (A), and can be selected from known radical-polymerizable vinyl monomers as materials for plastic rod lenses.
Examples of the radical polymerizable vinyl monomer (B) include methyl methacrylate (n = 1.49, n represents a refractive index when a homopolymer is used; the same applies hereinafter); styrene (n = 1.59). ); Chlorostyrene (n = 1.61); vinyl acetate (n = 1.47); 2,2,3,3-tetrafluoropropyl (meth) acrylate, 2,2,3,3,4,4, Fluorinated alkyl such as 5,5-octafluoropentyl (meth) acrylate, 2,2,3,4,4,4-hexafluorobutyl (meth) acrylate, 2,2,2-trifluoroethyl (meth) acrylate (Meth) acrylate (n = 1.37 to 1.44); (meth) acrylates having a refractive index n = 1.43 to 1.62, such as ethyl (meth) acrylate, phenyl (meth) acrylate, benzine (Meth) acrylate, hydroxyalkyl (meth) acrylate, alkylene glycol (meth) acrylate, trimethylolpropane di or tri (meth) acrylate, pentaerythritol di, tri or tetra (meth) acrylate, diglycerin tetra (meth) acrylate, Dipentaerythritol hexa (meth) acrylate, fluorinated alkylene glycol poly (meth) acrylate, tricyclo [5.2.1.0 ^2,6 ] decanyl-8- (meth) acrylate; diethylene glycol bisallyl carbonate; .

The radical polymerizable vinyl monomer (B) contained in one kind of uncured material may be one kind or a combination of two or more kinds. The refractive index after curing of the uncured product can be controlled by the type and content of the radical polymerizable vinyl monomer (B).
In order to obtain good compatibility between the polymer (A) and the radical polymerizable vinyl monomer (B), the monomer used for the production of the polymer (A) and the radical polymerizable vinyl monomer ( It is preferable that at least one monomer contained in common in both monomers used as B) exists. The mass ratio of the polymer (A) and the radical polymerizable vinyl monomer (B) can be, for example, 30 to 41:70 to 59.

[Curing treatment]
In order to cure the filament that is a laminate of the uncured material, a thermosetting catalyst or a photocuring catalyst is added to the uncured material, and a heat curing treatment and / or a photocuring treatment is performed. Such a treatment causes a polymerization reaction of monomers present in the uncured product. As the thermosetting catalyst, a peroxide-based or azo-based catalyst or the like is used. As photocuring catalysts, benzophenone, benzoin alkyl ether, 4'-isopropyl-2-hydroxy-2-methylpropiophenone, 1-hydroxycyclohexyl phenyl ketone, benzyl methyl ketal, 2,2-diethoxyacetophenone, chlorothioxanthone, thioxanthone Compounds, benzophenone compounds, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, N-methyldiethanolamine, triethylamine and the like.

The thermosetting treatment can be performed by heat-treating an uncured product containing a thermosetting initiator for a predetermined time in a curing processing section such as a heating furnace controlled at a constant temperature.
The photocuring treatment can be performed by a method in which an uncured material containing a photocuring catalyst is irradiated with ultraviolet rays from the surroundings. Examples of the light source used for the photocuring treatment include a carbon arc lamp that generates light having a wavelength of 150 to 600 nm, a high-pressure mercury lamp, a medium-pressure mercury lamp, a low-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a chemical lamp, a xenon lamp, and a laser beam. Further, these light sources may be used in appropriate combination in order to increase the polymerization rate.

A rod lens is obtained by stretching a rod lens yarn obtained by curing the filamentous body as necessary, and then cutting it to a predetermined length.
The rod lens of the present invention, as shown in the examples described later, can sufficiently suppress thermal shrinkage even when exposed to a high temperature environment, and the thermal fluctuation of the conjugate length is small. Therefore, a good resolution can be maintained even when used in a high temperature environment.

[Rod lens array]
A plurality of rod lenses thus obtained are fixed between two substrates in a state in which the central axes of the rod lenses are arranged in a substantially parallel direction (referred to as a rod lens array). A rod lens array is obtained. One rod lens array constituting one rod lens array may be one row or two or more rows. Adjacent rod lenses may be in close contact with each other, or may be arranged with a certain gap.
The substrate may be flat or may be provided with grooves such as a U-shape or a V-shape for arranging and storing rod lenses at regular intervals. Although the material of a board | substrate is not specifically limited, It is preferable that it is a material easy to process in the process of producing a rod lens array.
As the material of the substrate, various thermoplastic resins, various thermosetting resins, etc. are preferable. Acrylic resin, phenolic resin, ABS resin (acrylonitrile-butadiene-styrene copolymer), polyimide resin, liquid crystal polymer, epoxy resin Resins are particularly preferred. Further, as the base material or reinforcing material of the substrate, fibers or paper may be used, and a release agent, a dye, a pigment or the like may be added to the substrate.

The means for fixing the rod lens between the substrates is not particularly limited as long as it is an adhesive having an adhesive force or adhesive strength that can stick the rod lens and the substrate or the rod lenses. In the present specification, the adhesive and the pressure-sensitive adhesive are referred to as “adhesive” without distinction.
For example, an adhesive that can be applied in a thin film, a spray adhesive, a hot-melt adhesive, or the like can be used. As a method for applying the adhesive to the substrate or the rod lens, a known coating method such as coating with a coater, screen printing method, spray coating method or the like can be used depending on the type of the adhesive.

  Since the above rod lens is used in the plastic rod lens array of the present invention, the rod lens array is excellent in heat resistance, and even when used in a high temperature environment, thermal contraction of the rod lens is suppressed and the conjugate length hardly changes. Therefore, a good resolution can be obtained even when used in a high temperature environment. Therefore, for example, it can be suitably used for a high-resolution image sensor or LED printer of 600 dpi or more.

EXAMPLES The present invention will be specifically described below using examples, but the present invention is not limited to these examples. In the following examples, the following measurement methods or evaluation methods were used.
<Refractive index distribution>
The measurement was performed using an Interfaco interference microscope manufactured by Carl Zeiss.
<Conjugate length and resolution (average MTF, MTF fluctuation rate)>
Using a grating pattern having a spatial frequency of 12 (line pair / mm, Lp / mm), light (525 nm) from a light source is incident on the rod lens array whose both end surfaces perpendicular to the optical axis are polished through the grating pattern to form an image. The lattice image was read by a CCD line sensor installed on the surface, the maximum value (i _max ) and the minimum value (i _min ) of the measured light quantity were measured, and MTF (Moderation Transfer Function) was obtained by the following equation.
MTF (%) = {(i _max −i _min ) / (i _max + i _min )} × 100

At that time, the distance between the grating pattern and the entrance end of the rod lens array and the distance between the exit end of the rod lens array and the CCD line sensor were made equal. Then, the MTF was measured by moving the grating pattern and the CCD line sensor symmetrically with respect to the rod lens array, and the distance between the grating pattern and the CCD line sensor when the MTF was the best was defined as the conjugate length.
Also, the distance between the grating pattern and the CCD line sensor is fixed at a conjugate length, the entire width of the rod lens array is scanned, MTF is measured at 50 points, the average value and the standard deviation are obtained, the resolution and its variation index, did.
Here, the spatial frequency indicates a combination of white lines and black lines as one line, and indicates how many combinations of these lines are provided within a width of 1 mm.

<Heat resistance test>
The rod lens array was placed in a dryer set at 80 ° C. (relative humidity 30% or less) and heated by a method of holding for 1000 hours. Before and after heating, the conjugate length, MTF average value, and standard deviation were measured by the above methods, respectively, and evaluated according to the following criteria.
◎ when the absolute value of the difference between the conjugate length [mm] before heating and the conjugate length [mm] after heating is 0.2 mm or less, ◯ when 0.3 mm or more and 0.4 mm or less, and 0.5 mm or more The case of is evaluated as x.
The case where the average MTF [%] after heating is 70% or more is evaluated as ◎, the case where it exceeds 60% and less than 70% is evaluated as ○, and the case where it is 60% or less is evaluated as ×.
The case where the value of MTF fluctuation rate [%] after heating is 4% or less is evaluated as ◎, the case where it is 5% or more and 6% or less is evaluated as ◯, and the case where it is 7% or more is evaluated as ×.
The MTF fluctuation rate (unit:%) is a value obtained by standard deviation / MTF average value × 100.

[Examples 1 and 2 and Comparative Example 1]
Components shown in Table 1 below were blended to prepare stock solutions for forming the first to fifth layers. The unit of the blending amount shown in Table 1 is “part by mass”.
The polymers and monomers shown in Table 1 are as follows.
-Polymer (A-1): A copolymer obtained by polymerizing a monomer mixture comprising 60 parts by mass of methyl methacrylate, 20 parts by mass of styrene and 20 parts by mass of maleic anhydride. This copolymer comprises a structural unit derived from methyl methacrylate (the following formula (a)), a structural unit derived from styrene (the following formula (b)), and a structural unit derived from maleic anhydride (the following formula (c )).
-Polymer (A-2): A copolymer obtained by polymerizing a monomer mixture consisting of 70 parts by mass of methyl methacrylate, 20 parts by mass of styrene, and 10 parts by mass of maleic anhydride. This copolymer is also composed of structural units represented by the following formulas (a), (b) and (c).
PMMA: polymethyl methacrylate.
MMA: methyl methacrylate.
TCDMA: tricyclo [5.2.1.0 ^2,6 ] decanyl-8-methacrylate represented by the following formula (i).
8FM: 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate.

The stock solution of each layer was prepared by adding 0.25 parts by mass of 1-hydroxycyclohexyl phenyl ketone as a photocuring initiator and 0.1 parts by mass of hydroquinone (HQ) as a polymerization inhibitor to the polymers and monomers shown in Table 1. Part was added, and it prepared by the method of heat-kneading at 70 degreeC.
Further, for the purpose of suppressing crosstalk light and flare light, 0.57 mass of dye Blue ACR (manufactured by Nippon Kayaku Co., Ltd.) is further added to each stock solution for the fourth layer and the fifth layer before heating and kneading. Parts, dye MS Yellow HD-180 (manufactured by Mitsui Chemicals Dye) and MS Magenta HM-1450 (manufactured by Mitsui Chemicals Dye) 0.14 parts by mass, dye Diaresin Blue 4G (Mitsubishi Chemical Co., Ltd.) Product) and Kayasorb CY-10 (manufactured by Nippon Kayaku Co., Ltd.) were added in an amount of 0.02 parts by mass.

  Five kinds of stock solutions for the first layer to the fifth layer were simultaneously extruded from a concentric five-layer composite spinning nozzle to form a filament. The temperature of the composite spinning nozzle was 54 ° C. Among the first to fifth layers, the refractive index of the first layer stock solution is the highest, the refractive index of the fifth layer stock solution is the lowest, and the thickness of each layer in the diameter direction (1) when ejected from the nozzle In the layer, the ratio of radius) was set so that the first layer / second layer / third layer / fourth layer / fifth layer = 18/49/28/3/2.

The filaments extruded from the composite spinning nozzle are photocured by light irradiation while mutually diffusing in the first curing treatment unit. Next, in the second curing processing part, the polymerization is completed by powerful light irradiation.
In the first curing processing section, 18 chemical lamps having a length of 120 cm and 40 W are arranged at equal intervals around the central axis, and the filamentous body moves on the central axis. In the second curing section, three 2 KW high-pressure mercury lamps are arranged at equal intervals around the central axis, and the filamentous body moves on the central axis.
The filamentous body passes through these hardened portions while being taken up by a nip roller, and becomes a rod lens raw yarn.

The center refractive index of the obtained rod lens was 1.512 in Examples 1 and 2, and 1.498 in Comparative Example 1. In any of the examples, the refractive index distribution was approximated by the formula (1) in the range of 0.2r to 0.8r from the central axis toward the outer periphery. Refractive index distribution constant g at 525nm wavelength, Example 1 is 0.43 mm ^-1, Example 2 is 0.45 mm ^-1, Comparative Example 1 was 0.48 mm ^-1.
In each example, a dye-mixed layer having a thickness of about 15 μm from the outer peripheral surface of the rod lens toward the center is formed.
In each example, a large number of the obtained rod lenses were used to produce a single-row rod lens array (lens length of 8.0 mm) with an array pitch of 0.62 mm (gap 20 μm between adjacent lenses).
The conjugate length, MTF average value, and MTF fluctuation rate at 525 nm of the obtained rod lens array were measured and evaluated by the above methods. The results are shown in Table 2.

From the results in Table 2, both the rod lens arrays of Example 1 and Example 2 have small changes in conjugate length due to heating, good average MTF value and MTF fluctuation rate after heating, and excellent heat resistance. Yes.
Compared to this, the rod lens array of Comparative Example 1 has a large change in conjugate length before and after heating, and the average MTF value greatly decreases and the MTF fluctuation rate increases due to heating. Compared to heat resistance.
Moreover, when Example 1 and Example 2 are compared, the direction of Example 1 with much content of the acid anhydride type monomer in the monomer mixture used for manufacture of a polymer (A) is before and behind a heating. The change in the conjugate length and the average MTF value is smaller, and the heat resistance is better. From this, it is thought that the structural unit derived from the acid anhydride monomer of the polymer (A) present in the rod lens contributes to the improvement of heat resistance.

  The plastic rod lens of the present invention and the plastic rod lens array using the plastic rod lens are components for various scanners such as hand scanners; components for image sensors in copying machines, facsimiles, etc .; various printers such as LED printers. It is suitably used as a component for various optical transmission bodies such as a component for a writing device.

Claims (2)

  A plastic rod lens obtained by curing an uncured product containing a polymer (A) having a structural unit derived from an acid anhydride monomer and a radical polymerizable vinyl monomer (B).   A plurality of plastic rod lenses according to claim 1, comprising at least one rod lens array arranged and fixed so that the central axes of the rod lenses are substantially parallel to each other between two substrates. Rod lens array.